The present invention relates generally to an electronic camera designed to phototake a subject using a two- dimensional image pickup device, and more particularly to an electronic still camera comprising a display means for displaying an electronic image while it is phototaken or after it has been phototaken.
So far, an optical finder and an electronic view finder have been known for an electronic still camera finder.
A typical optical finder is disclosed in EP0722106A2. An optical system designed to view an external image while a liquid crystal display field frame is superposed on the external image is disclosed in JP-A 8-201912.
With both finders, however, it is impossible to view a phototaken electronic image through them because they are of the type that an external object is viewed through them apart from the electronic image phototaken by an phototaking optical system.
Some electronic view finders comprising a liquid crystal display element of small size to be attached to a back side of a camera body are disclosed in JP-A""s 8-46834 and 8-51561. A loupe optical system designed to magnify and display an electronic image displayed a display element is also available.
One problem with the aforesaid electronic view finder of the direct view type that a two-dimensional display element is attached to the back side of the camera body is that the two-dimensional display element used must be of small size because it is impossible to increase the size of the camera body. Another problem is that when a high-precision image is displayed, it is difficult to take a full view of the image with the naked eye because the display screen used is too small. With the loupe optical system, on the other hand, it is difficult to achieve a compact electronic camera because the axial size of the loupe, that is, the size of the loupe in the depth direction of the camera becomes large.
In view of such problems associated with the prior art, an object of the present invention is to provide a compact electronic camera designed to display an electronic image on a two-dimensional display element while it is phototaken or after it has been phototaken and magnify the thus displayed image in the form of a virtual image using a compact magnifying optical system comprising a curved reflecting mirror, so that the phototaken image can be viewed with high precision.
According to the present invention, the aforesaid object is achieved by the provision of an electronic camera comprising a phototaking optical system, a two-dimensional image pickup element for receiving an object image formed by said phototaking optical system, a two-dimensional display element for displaying said object image in the form of an image to be viewed, and a magnifying optical system for guiding said image to a viewer""s eyeball, wherein said magnifying optical system includes a first reflecting surface for turning back an optical path between said two-dimensional display element and said viewer""s eyeball to achieve compactness, said first reflecting surface being defined by a curved surface having an action to magnify said image.
Preferably in this case, the magnifying optical system further includes a second reflecting surface located in opposition to the first reflecting surface to turn back an optical path between the first and second reflecting surfaces, thereby making a distance between the two-dimensional display element and the viewer""s eyeball short.
The first and second reflecting surfaces may be provided by a prism member made up of a transparent medium having a refractive index (n) greater than 1.3 (n greater than 1.3).
In this case, the first reflecting surface may be formed on one surface of the prism member while the second reflecting surface is located at a position of the prism member such that the medium is sandwiched between the first and second reflecting surfaces.
Further, the second reflecting surface may behave as a combined transmitting and reflecting surface.
It is desired that at least one of the first and second reflecting surfaces be defined by a rotationally asymmetric surface having an action to make correction for aberrations produced by decentration.
Furthermore in that case, the two-dimensional image pickup element may be located in opposition to the two-dimensional display element.
The magnifying optical system may have two actions, one to guide an image displayed on the two-dimensional display element to the viewer""s eyeball and the other to guide object light phototaken by the phototaking optical system directly to the viewer""s eyeball.
The electronic camera of the invention may further comprise between the two-dimensional image pickup element and the two-dimensional display element a signal processing circuit, a controller, a driver and a recording/reproducing unit so that the object image received at the two-dimensional image pickup element is recorded in the recording/reproducing unit upon photoelectric conversion and, at the same time, is displayed on the two-dimensional display element by the driver via the controller during phototaking, and, upon phototaking, a signal recorded in the recording/reproducing unit is reproduced to display an electronic image on the two-dimensional display element by the driver via the controller.
Reference is made to why the aforesaid arrangements are adopted in the invention, and how they work. In the invention, the magnifying optical system for projecting a virtual image form of electronic image on a magnified scale is constructed of at least one curved reflecting mirror and a surface having a combined transmitting and reflecting action, so that an eyepiece optical system having a large exit pupil diameter can be achieved. This, in turn, makes it possible to display an electronic image on the two-dimensional display element during or after phototaking so that it can be easily viewed in a virtual image form through the magnifying optical system.
If, in the invention, the magnifying optical system is be constructed of a prism body comprising a transparent medium having a refractive index of at least 1, the magnifying optical system can then be easily assembled because the reflecting surface can be integrated with the surface having a combined transmitting and reflecting action.
If, in the invention, the curved reflecting surface of the magnifying optical system is constructed of a back-surface mirror, it is then possible to reduce the curvature of the curved reflecting mirror (or increase the radius of curvature thereof), thereby reducing aberrations produced at the reflecting surface. This, in turn, makes it possible to reduce an aberration change upon movement of the viewer""s eyeball and, hence, provide an easy-to-view electronic image of high precision.
Here let f (mm) denote the focal length of the magnifying optical system. It is then desired to satisfy
f less than 30xe2x80x83xe2x80x83(1)
In other words, the overall size of the electronic camera according to the invention can be reduced by shortening the magnifying optical system. A problem with a conventional finder optical system using a transmitting lens system is that the focal length of an eyepiece optical system cannot be made short because some considerable aberrations occur due to the fact that a main power for the optical system is obtained by a transmitting surface.
It is more preferable to satisfy
f less than 20xe2x80x83xe2x80x83(2)
This is because the optical system of smaller size can be achieved.
Here let L (mm) represent the diagonal length of the two-dimensional display element. It is then desired to satisfy
L less than 25xe2x80x83xe2x80x83(3)
In other words, the size of the electronic camera according to the invention can be reduced by reducing the magnitude of the opposite angle of the two-dimensional display element in the finder optical system. It is thus important to satisfy condition (3). If L greater than 25, the size of a two-dimensional display element built in an electronic camera then becomes too large to reduce the size of the electronic camera.
It is more preferable to satisfy
L less than 18xe2x80x83xe2x80x83(4)
It is most preferable to satisfy
L less than 15xe2x80x83xe2x80x83(5)
If, in the invention, the electronic view finder is used in combination with an optical finder, it is then possible to achieve an electronic camera of smaller size that is the object of the invention. In this case, it is possible to display a previously phototaken image and an object image being phototaken in a superposed fashion. It is also possible to synthesize an object image and a previously phototaken electronic image or phototake an image through the finder while position information is displayed.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.